As an example of a gas combustion type driving tool, there is known a combustion gas drive type driving tool in which combustible gas is charged into a combustion chamber formed in a hermetically closed manner within a tool body to stir up a mixed gas composed of combustible gas and air within the combustion chamber, a stirred mixed gas is combusted within the combustion chamber to thereby generate a high pressure combustion gas, and the high pressure combustion gas is applied to a striking piston accommodated within a striking cylinder to thereby impactively drive the striking piston within the striking cylinder, whereby a nail supplied to a nose part disposed in the lower portion of the tool body can be driven into steel or concrete by a driver connected to the lower surface side of the drive piston. (JP-A-08-252806) In such combustion gas type driving tool, not only a container such as a gas cylinder filled with combustible gas is mounted into the tool but also a battery functioning as a power supply for igniting the combustible gas is mounted on the tool, thereby forming the tool as a portable tool. Thus, this type of driving tool can carry out an operation to drive a nail or a pin without being restrained by a power supply source for supplying power, such as compressed air or the like.
In the above-mentioned gas combustion type driving tool, there is provided a feed device which sequentially feeds connected fasteners accommodated in a magazine into the nose part. As a feed device of this type, there is known a device structured such that connected fasteners, which are composed of a large number of fasteners connected together in a straight line, are accommodated in a sheath-shaped magazine, the connected fasteners are normally pressed toward the nose part by a spring having a constant output and, immediately after a fastener supplied to an eject opening formed in the nose part is driven, a next faster is supplied into the nose part.
However, in this straight-shaped magazine, since the number of fasteners to be accommodated therein is small, it has been requested to mount a cylindrical-shaped magazine which can store a large number of connected fasteners wound in a coil-like shape. Here, as a feed device used to feed the fasteners accommodated in the cylindrical-shaped magazine, generally, there is known a feed piston/cylinder device. This is a device in which, on a feed piston slidably accommodated in a feed cylinder, there is provided a feed claw engageable with and removable from the connected fasteners accommodated in the magazine, and the feed claw is reciprocated in a feed direction for feeding the feed claw toward the nose part side and in a retreat direction opposite to the feed direction.
Thus, it is possible to employ cylindrical-shaped magazine together with the previously described feed piston/cylinder device. In this case, it can be expected that the feed piston of the feed piston/cylinder device is made to reciprocate using a spring and the pressure of combustion gas in a combustion chamber. Referring further to the reciprocating operation, the feeding operation of the feed piston is executed by a spring, while the retreating operation of the feed piston is executed using the pressure of the combustion gas.
However, in a structure where a combustion chamber and a feed cylinder are directly connected to each other, as shown in FIG. 13, the combustion gas is applied to both of the striking piston and feed piston (feed claw) substantially at the same time; therefore, almost simultaneously with the striking operation of the striking piston, the feed piston is also retreated, thereby causing the fasters to be unstable in attitude when they are driven. In other words, since the feed piston is caused to remain at a feed position due to the spring and the leading one of the fastener supplied into the nose part is thereby pressed by the feed claw, the leading faster is stabilized in attitude. While the fasteners are being driven out by a driver, preferably, the attitudes of the fasteners may be stable. However, when a striking device is actuated due to the pressure of the combustion gas and thus the driver is driven together with a striking piston whereby the faster is driven and the piston is retreated simultaneously, a force for pressing and holding the fastener is lost to thereby cause the faster to be unstable in attitude, which makes it impossible to positively drive the fastener in its proper attitude.
In view of this, as means for delaying the operation timing of the striking piston of the striking device, there is known a technology in which, by taking out the combustion gas from the striking cylinder at a position slightly lower than the top dead center of the striking piston, the operation timing of the striking piston is delayed.
However, at the position slightly lower than the top dead center of the striking piston, the pressure of the combustion gas is reduced slightly, which in turn reduces the pressure to be applied to the feed cylinder of the feed device. This makes it necessary to increase the quantity of gas to be supplied into the feed cylinder, which also results in the increased size of the feed device.